View Full Cisco CCNP Service Provider 300-510 Exam Dumps and Practice Test Dumps

 

Question 221. An IS-IS router on a broadcast LAN is elected as the Designated Intermediate System (DIS). Which function is specifically associated with the DIS?

1. Establishing BGP sessions with all routers on the LAN
2. Translating OSPF Type 7 LSAs
3. Assigning MPLS VPN Route Targets
4. Generating a pseudonode LSP to represent the broadcast network

Correct Answer: 4. Generating a pseudonode LSP to represent the broadcast network

Explanation :-

In IS-IS, the Designated Intermediate System (DIS) is elected on broadcast multiaccess networks to improve the efficiency of link-state database representation. The DIS creates a pseudonode LSP that represents the shared LAN segment and its connected routers. This avoids requiring every router on the LAN to advertise individual point-to-point relationships with every other router. The DIS role is different from the OSPF DR/BDR mechanism, although both reduce control-plane overhead on multiaccess networks. DIS election and pseudonode LSP generation are specific IS-IS functions and are important when troubleshooting database synchronization on broadcast segments.

Question 222. An OSPF NSSA contains an ASBR that redistributes an external route. Routers outside the NSSA must learn the route as a normal external route. What process is required at the NSSA boundary?

1. Type 5 LSAs are converted into Type 2 LSAs
2. Type 7 LSAs are translated into Type 5 LSAs
3. Type 3 LSAs are translated into Type 4 LSAs
4. Type 1 LSAs are converted into Type 3 LSAs

Correct Answer: 2. Type 7 LSAs are translated into Type 5 LSAs

Explanation :-

External routes redistributed inside an OSPF NSSA are represented by Type 7 LSAs. To advertise those routes beyond the NSSA, an NSSA ABR can translate the appropriate Type 7 LSAs into Type 5 external LSAs. The Type 5 LSAs can then be flooded through normal OSPF areas according to the applicable rules. This translation allows an NSSA to support external route redistribution without permitting the same unrestricted external LSA flooding associated with a standard area. The Type 7-to-Type 5 translation process is therefore an important troubleshooting consideration when external routes are visible inside an NSSA but missing elsewhere.

Question 223. A provider wants to reduce the impact of a single link failure in an OSPF network by calculating a loop-free alternate path in advance. Which OSPF capability is intended for this purpose?

1. LFA
2. Route dampening
3. BGP Add-Path
4. Prefix aggregation

Correct Answer: 1. LFA

Explanation :-

Loop-Free Alternate (LFA) is a fast-reroute mechanism that allows an OSPF router to precompute an alternate next hop that can be used when the primary path fails. By having a repair path available before a failure occurs, traffic can be redirected without waiting for the complete IGP convergence process. LFA is particularly useful for improving convergence in service-provider networks. BGP Add-Path provides multiple BGP paths, route dampening addresses route instability, and prefix aggregation reduces routing-table size. These mechanisms do not directly provide the same precomputed IGP fast-reroute function as LFA.

Question 224. An IS-IS router receives a newer LSP from a neighbor and determines that its local copy has an older sequence number. Which protocol message can be used to request the newer LSP?

1. Hello PDU
2. CSNP
3. PSNP
4. BGP UPDATE

Correct Answer: 3. PSNP

Explanation :-

IS-IS uses Partial Sequence Number PDUs (PSNPs) to acknowledge or request specific LSP information. If a router determines that it is missing a newer version of an LSP, it can use a PSNP to request the required information from a neighboring router. Complete Sequence Number PDUs (CSNPs) provide a summary of the LSP database and are commonly used for synchronization, particularly on broadcast networks. Hello PDUs establish and maintain IS-IS adjacencies, while BGP UPDATE messages belong to BGP rather than IS-IS. Understanding CSNP and PSNP interaction is essential for diagnosing IS-IS database synchronization problems.

Question 225. A BGP router uses a route reflector to distribute routes between iBGP clients. A route learned from one client is advertised to another client. What is the primary purpose of this design?

1. To replace the IGP entirely
2. To reduce the need for a full-mesh iBGP topology
3. To encrypt BGP UPDATE messages
4. To eliminate all BGP path attributes

Correct Answer: 2. To reduce the need for a full-mesh iBGP topology

Explanation :-

Route reflection provides a scalable alternative to a full-mesh iBGP design. A route reflector can receive routes from its clients and advertise appropriate routes to other clients, allowing a larger autonomous system to operate without requiring every iBGP router to maintain a direct session with every other iBGP router. The route reflector does not replace the underlying IGP, encrypt BGP messages, or remove BGP path attributes. Instead, it changes how iBGP routes are distributed. Route reflection is therefore particularly useful in large service-provider networks where maintaining a complete iBGP mesh would create substantial operational overhead.

Question 226. A BGP route reflector receives a route from an iBGP client and reflects it to another client. Which attribute helps prevent routing loops involving route reflectors?

1. LOCAL_PREF
2. MED
3. ORIGIN
4. CLUSTER_LIST

Correct Answer: 4. CLUSTER_LIST

Explanation :-

The CLUSTER_LIST attribute is used by BGP route reflection to help prevent routing loops. When a route reflector reflects a route, it adds its cluster ID to the CLUSTER_LIST. If the route later returns to a route reflector that sees its own cluster ID in the list, it can reject the route rather than reflect it again. This provides loop-prevention protection in route-reflector topologies. LOCAL_PREF influences path selection, MED can influence path selection between neighboring autonomous systems, and ORIGIN identifies how a route was introduced into BGP. None of these performs the specific route-reflector cluster-loop prevention function.

Question 227. A service provider wants to advertise a customer route to an external peer but prevent the peer from advertising that route to other autonomous systems. Which BGP community should be applied?

1. NO_ADVERTISE
2. INTERNET
3. NO_EXPORT
4. LOCAL_PREF

Correct Answer: 3. NO_EXPORT

Explanation :-

The NO_EXPORT community tells a receiving BGP speaker not to advertise the associated route outside its own autonomous system or applicable confederation boundary. This allows the immediate BGP peer to receive and use the route while limiting further external propagation. NO_ADVERTISE imposes a stronger restriction because the receiving BGP speaker should not advertise the route to any BGP peer. INTERNET represents normal advertisement behavior, while LOCAL_PREF is an internal BGP path-selection attribute. NO_EXPORT is therefore appropriate when the route should remain within the receiving autonomous system.

Question 228. An administrator wants to influence inbound traffic by making a provider’s advertised path appear longer to external BGP neighbors without changing the actual physical topology. Which technique is commonly used?

1. AS_PATH prepending
2. Increasing LOCAL_PREF
3. Changing the BGP router ID
4. Enabling BFD

Correct Answer: 1. AS_PATH prepending

Explanation :-

AS_PATH prepending adds additional copies of the local autonomous system number to an advertised BGP route. This makes the AS_PATH appear longer to external BGP neighbors and can influence their path-selection process when AS_PATH length is considered. It is commonly used as an inbound traffic-engineering technique because the provider is attempting to make one advertised path less attractive to external networks. LOCAL_PREF is primarily used within an autonomous system to influence outbound path selection. BFD provides failure detection, while the router ID identifies the BGP speaker and does not directly manipulate path length.

Question 229. A provider has multiple BGP paths to the same destination and wants to select the route with the shortest AS_PATH after higher-priority BGP attributes have been compared. Which route is preferred?

1. The route with the highest MED
2. The route with the oldest BGP session
3. The route learned from iBGP
4. The route with the shortest AS_PATH

Correct Answer: 4. The route with the shortest AS_PATH

Explanation :-

AS_PATH length is an important BGP best-path attribute. When the higher-priority attributes have not already selected a path, BGP generally prefers the path with the shorter AS_PATH because it represents fewer autonomous-system hops. This does not mean AS_PATH is always the first attribute considered; attributes such as LOCAL_PREF and other earlier criteria can determine the best path before AS_PATH is evaluated. MED, eBGP/iBGP status, and later tie-breakers are considered according to the applicable best-path algorithm. Engineers should therefore evaluate the complete BGP decision process rather than treating AS_PATH as the only factor.

Question 230. A PE router receives an MPLS VPN packet containing a VPN label. What does that VPN label primarily help the PE identify?

1. The BGP autonomous system number
2. The appropriate VPN or VRF forwarding context
3. The OSPF area ID
4. The IS-IS DIS priority

Correct Answer: 2. The appropriate VPN or VRF forwarding context

Explanation :-

In an MPLS L3VPN, the VPN label provides information that allows the egress PE router to identify the appropriate VPN forwarding context, typically the corresponding VRF or VPN route. The transport label is used to carry the packet across the MPLS provider core toward the egress PE, while the VPN label provides service-specific forwarding information at the edge. BGP carries the VPN route and associated label information through MP-BGP. OSPF area IDs, IS-IS DIS priorities, and BGP autonomous system numbers do not serve as the packet’s VPN forwarding label.

Question 231. An enterprise connects to two service providers and wants the local BGP router to prefer one provider’s exit path for outbound traffic. Which attribute can be configured locally and propagated through iBGP to influence this decision?

1. MED
2. AS_PATH
3. LOCAL_PREF
4. Originator ID

Correct Answer: 3. LOCAL_PREF

Explanation :-

LOCAL_PREF is designed to influence outbound path selection within an autonomous system. A higher LOCAL_PREF is preferred, assuming the competing paths reach the relevant stage of the BGP decision process. Because LOCAL_PREF is propagated through iBGP, an organization can establish a consistent preference for one provider exit across its internal BGP speakers. AS_PATH manipulation is more commonly used to influence how external networks select inbound paths. MED is used for certain inter-AS path-selection scenarios, while Originator ID is associated with route reflection. LOCAL_PREF is therefore the appropriate attribute for this outbound preference requirement.

Question 232. A network uses PIM-SM and has receivers interested in multicast group 239.1.1.1. Before the source-specific (S,G) state is established, which shared-tree state commonly represents the receiver’s interest?

1. (*,G)
2. (S,*)
3. (S,G,R)
4. (G,*)

Correct Answer: 1. (*,G)

Explanation :-

In PIM Sparse Mode, (*,G) represents shared-tree state for a multicast group without specifying a particular source. Receivers initially join the shared tree rooted at the Rendezvous Point when operating in the traditional ASM model. Once traffic from a source is received and source-specific forwarding is established, the network can create (S,G) state and potentially switch to the shortest-path tree. The asterisk in (*,G) indicates that the state applies to any source for the specified group. This distinction is important when interpreting multicast routing tables and troubleshooting PIM-SM forwarding.

Question 233. A service provider is deploying Segment Routing and wants a SID that represents a node-level destination, allowing traffic to follow the shortest path toward that node according to the IGP. Which SID should be used?

1. Adjacency SID
2. Binding SID
3. Anycast SID
4. Node SID

Correct Answer: 4. Node SID

Explanation :-

A Segment Routing Node SID identifies a node and is normally associated with a prefix representing reachability to that node. When a packet is sent using a Node SID, the underlying IGP topology determines the path toward the destination node unless additional segments impose further constraints. An Adjacency SID identifies a particular link or adjacency, making it suitable for explicit link-level steering. A Binding SID identifies a Segment Routing policy or bound segment list, while an Anycast SID can represent a shared endpoint. Node SIDs are fundamental to Segment Routing shortest-path forwarding.

Question 234. A BGP neighbor is configured, but the session remains in the Active state. The administrator confirms that the peer IP address is correct and asks what should be checked next. Which underlying condition is particularly important?

1. The BGP community value
2. TCP/IP reachability to the peer address
3. The MPLS VPN Route Target
4. The OSPF DR priority

Correct Answer: 2. TCP/IP reachability to the peer address

Explanation :-

A BGP session depends on an underlying TCP connection, so IP reachability between the BGP peers must be established before the session can reach Established state. The Active state often indicates that BGP is attempting to establish or re-establish the TCP connection. Engineers should verify routing-table entries, source-interface or loopback reachability, access-control policies, and relevant TCP connectivity. Route Targets and BGP communities influence routing policy rather than basic TCP session establishment. OSPF DR priority is unrelated to BGP TCP connectivity. Troubleshooting the underlying IP path is therefore an important next step.

Question 235. An administrator wants to prevent an internal BGP route from being advertised to any BGP peer after applying a well-known community. Which community provides this behavior?

1. NO_ADVERTISE
2. NO_EXPORT
3. INTERNET
4. NOPEER

Correct Answer: 1. NO_ADVERTISE

Explanation :-

The NO_ADVERTISE well-known BGP community indicates that a route should not be advertised to any BGP peer. This is more restrictive than NO_EXPORT, which allows the receiving autonomous system to use the route internally while preventing further external advertisement. The distinction is important when designing route-propagation policies. INTERNET represents the normal default community behavior, while NOPEER has a different purpose and is not the standard answer for preventing all BGP advertisements. Applying NO_ADVERTISE can therefore provide explicit control when a route must remain local to the receiving BGP speaker.

Question 236. A network engineer needs to advertise IPv6 VPN routes between PE routers across an MPLS provider network. Which MP-BGP address family is specifically associated with IPv6 VPN routes?

1. IPv4 unicast
2. VPNv4
3. VPNv6
4. IPv6 link-local

Correct Answer: 3. VPNv6

Explanation :-

The VPNv6 address family is used by MP-BGP to exchange IPv6 VPN routes between provider-edge routers. Similar to VPNv4 for IPv4-based MPLS L3VPNs, VPNv6 combines IPv6 VPN prefixes with the information required for VPN route distribution and forwarding. Route Distinguishers provide uniqueness for overlapping prefixes, while Route Targets control VRF import and export policy. IPv4 unicast is not the appropriate VPN address family, and IPv6 link-local addresses are interface-local addressing constructs rather than an MP-BGP VPN address family.

Question 237. A service provider configures a BGP route policy that should advertise only the default route 0.0.0.0/0 to a customer. Which mechanism provides the most direct prefix-specific match?

1. BGP MED
2. A prefix list matching 0.0.0.0/0
3. BGP router ID
4. AS_PATH prepending

Correct Answer: 2. A prefix list matching 0.0.0.0/0

Explanation :-

A prefix list can explicitly match the default route 0.0.0.0/0, allowing a route policy to permit that route while denying other prefixes. This provides precise control over the advertisements sent to the customer. MED and AS_PATH prepending influence BGP path selection rather than directly selecting which prefixes are advertised. The BGP router ID identifies the BGP speaker and does not perform route filtering. When implementing a default-only advertisement policy, engineers should also ensure that the policy has an explicit deny or equivalent behavior for unwanted routes.

Question 238. An MPLS network uses LDP for label distribution. The LDP session between two routers is established, but the expected label-switched path is missing. Which factor should be verified because MPLS forwarding depends on underlying route reachability?

1. BGP community propagation only
2. OSPF DR election only
3. PIM Rendezvous Point configuration
4. IGP reachability to the relevant FEC and label bindings

Correct Answer: 4. IGP reachability to the relevant FEC and label bindings

Explanation :-

LDP distributes labels for Forwarding Equivalence Classes, but the resulting MPLS forwarding path also depends on underlying IP routing information. If the IGP does not provide reachability to the relevant destination or the expected label binding is missing, the router may not install the corresponding MPLS forwarding entry. Engineers should therefore inspect the IGP route, LDP bindings, LIB, and LFIB when troubleshooting a missing LSP. A successful LDP session alone does not guarantee that every expected FEC has a usable label-switched forwarding entry.

Question 239. A multicast network uses Anycast RP for redundancy. Two routers provide the RP function using the same anycast address, while MSDP is used between them. What is the primary purpose of this design?

1. To provide redundant RP functionality and synchronize source information
2. To replace all PIM interfaces with BGP
3. To eliminate the need for multicast routing
4. To create a separate MPLS VPN for each multicast group

Correct Answer: 1. To provide redundant RP functionality and synchronize source information

Explanation :-

Anycast RP allows multiple routers to share the same RP address, providing redundancy and enabling multicast receivers to use the topologically closest RP. MSDP can exchange source-active information between the RPs so that multicast sources learned through one RP can be known by the other. This design helps maintain multicast service when one RP becomes unavailable and distributes RP functionality across the network. Anycast RP does not replace PIM, eliminate multicast routing, or create MPLS VPNs. Its purpose is specifically associated with resilient Rendezvous Point deployment and source-information exchange.

Question 240. An engineer needs to protect a BGP session from receiving an unexpectedly large routing table caused by a customer route leak. Which configuration is most directly intended to limit the number of accepted prefixes?

1. BGP route reflection
2. BGP graceful restart
3. BGP maximum-prefix
4. BGP MED

Correct Answer: 3. BGP maximum-prefix

Explanation :-

BGP maximum-prefix allows an administrator to establish a threshold for the number of prefixes accepted from a BGP neighbor. If the number of received prefixes exceeds the configured limit, the router can take protective action according to the configured behavior. This is particularly valuable at service-provider customer boundaries because an accidental route leak can cause an unexpectedly large number of routes to be advertised. Route reflection addresses iBGP scalability, graceful restart supports continuity during certain control-plane events, and MED influences path selection. Maximum-prefix is therefore the direct protection mechanism for excessive received prefixes.